Malaria is caused by Plasmodium parasites and is transmitted to humans by female Anopheles mosquitoes. Current malaria control measures may not be sufficient to achieve effective control and elimination. There is an urgent need to advance our understanding of the vector's biological processes that can potentially be exploited in an effort to block malaria transmission. The mosquito's innate immunity plays a pivotal role in the interaction between the malaria parasites and the mosquito vector, and is a determining factor of vectorial capacity. In this study, we will identify microRNAs (miRNAs) used by mosquitoes to modulate their defense against Plasmodium infection and will determine whether manipulating the levels of the selected miRNAs can lead to enhanced mosquito resistance to Plasmodium infection. miRNAs are small endogenous RNA molecules that post-transcriptionally regulate gene expression. They recognize their target mRNA transcripts through partial sequence complementarity. miRNAs have been shown to act as master regulators by targeting multiple genes involved in the same biological process. Our preliminary studies clearly demonstrate that miRNAs are involved in modulating the mosquito defense response to malaria parasites. We have performed a genome-wide analysis of miRNA-mRNA interactions and discovered that the transcripts of some mosquito immune genes are differentially regulated by certain miRNAs in response to Plasmodium infection. We will investigate whether these identified miRNAs affect the survival of Plasmodium parasites, when and where the regulation takes place, and which genes are regulated (directly or indirectly) by the miRNAs during midgut invasion by Plasmodium ookinetes. The specific aims of this project are to: (1) Identify miRNA-mRNA interactions affected by P. falciparum infection of the midgut epithelium in An. gambiae, (2) Select miRNAs that play important regulatory roles in anti-Plasmodium defense, and (3) Use transgenic expression of miRNAs or miRNA sponges to enhance mosquito resistance to Plasmodium infection. Our proposed study addresses a serious gap in the understanding of miRNA function in mosquito- Plasmodium interactions, and may provide novel molecular targets for blocking malaria transmission.